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The A-Series ponds are located in the Buffer Zone on North Walnut Creek northeast of the Core Area. The ponds collect runoff from an approximately 380-acre basin that includes the northern portion of the Core Area and the Buffer Zone immediately north of the Core Area. Ponds A-I and A-2 are used for spill containment. Pond A-3 is used for detention of creek baseflow and stormwater runoff. Pond A-4 is used to store water before testing, treatment, and release to North Walnut Creek. All A-Series ponds also receive stormwater runoff from the tributary area directly surrounding the ponds. The following sections give the designations and general locations of the fifty sub-basins as used in the computer model analyses, and as further defined in Table III-I. Great Western Reservoir Drainal!e Basin The Great Western Reservoir drainage basin includes three land use areas for drainage planning purposes: the Buffer Zone, the Core Area, and the off-site area. The B-Series ponds are located in the Buffer Zone on South Walnut Creek, east of the Core Area. The ponds collect runoff from a 350-acre basin that includes the central portion of the Core Area and the Buffer Zone immediately east of the Core Area, north of the East Entrance Road. Ponds B-1 and B-2 are used for spill control. Pond B-3 receives sewage treatment plant effluent. Pond B-4 is used for detention of baseflow and stormwater runoff. Pond B-5 is used to store water before it is pumped to A-4. All B-Series ponds also receive stormwater runoff from the tributary area directly surrounding the ponds. Great Western Buffer Zone. The Great Western Buffer Zone includes sub-basins WADIV 1 to WADIV 4, SWA 1 to SWA 3, and WA 1 to WA 15. Descriptions of these sub-basins follow. The C-Series ponds are located along Woman Creek, south of the Core Area. Pond C-l is on Woman Creek, but is presently not used in water management because it is no longer a terminal pond. Pond C-2 is located off-stream of Woman Creek. The pond drains an approximately 190 acre basin through the South Interceptor Ditch. W ADIV 1 to W ADIV 4 - These sub-basins include those portions of the Rocky Flats Plant site Buffer Zone diverted into the Walnut Creek Diversion Canal. They include areas north of the West Entrance Road and west of the Core Area. Runoff from basin WAL 1 is routed through these basins. These basins outlet to sub-basin W A 5. Ponds D-l and D-2 are off-channel reservoirs in the southeast portion of the Buffer Zone that are fed by the Smart Ditch. They are not used for any water management functions on the plant site and hence were not analyzed in this study. SW A 1 to SW A 3 - These sub-basins lie east of the Core Area and north of the East Entrance Road. They include all of the Buffer Zone tributary to the B-Series ponds. Runoff from Core Area basins CSWAB and CSWAA is routed through these basins (see Section VII for a description of Core Area basins). The SWA sub-basins outlet to basin WA3. DRAINAGE BASIN DESIGNATIONS WA 1 to WA 15 - These sub-basins lie in the northeast portion of the Buffer Zone. They receive runoff from the WADIV sub-basins, SWA sub-basins, and all of the Core Area basins. These sub-basins end at the eastern boundary of the plant site at Indiana Street. They outlet into sub-basin GW 1 which lies east of Indiana Street. Sub-basins WA 9 and WA 10 form a separate tributary of Walnut Creek that feeds directly into Great Western Reservoir. For purposes of master drainage planning and ancillary use of the hydrologic models, the study area was first divided into three primary drainage basins: Great Western Reservoir, Standley Lake and Rock Creek. Next, the study area was defined further into four major drainage basins including Woman Creek basin, Walnut Creek basin, Upper Big Dry Creek basin and Rock Creek basin. For detailed hydrologic and hydraulic study, the study area was further defined as to basic land use and then divided into fifty sub-basins ranging in size from 2.56 to 0.011 square miles. The basin designations are shown on Figure III-2, sheet 1 and sheet 2.